IntroductionCOVID-19 pandemic has an impact on mortality indicators worldwide. Mitigation and repression actions to reduce the morbidity and mortality associated with the disease are necessary. However, they are criticised in the economic, social and psychological spheres. This social isolation, increased unemployment, routine changes, news of health complications and deaths related to COVID-19 can cause psychological repercussions that will certainly intensify in the coming months, and suicidal behaviour presents itself as a fatal outcome. It is necessary to know factors associated with suicidal behaviour in adults during the pandemic. Although there are studies, there is no systematic review to assess these factors, specifically in adults. The objective is to critically synthesise the scientific evidence on the factors associated with suicidal behaviour in adults in the COVID-19 pandemic.Methods and analysesA systematic review will be carried out, recommended by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol, in seven databases: Medical Literature Analysis and Retrieval System Online (MEDLINE), ISI of Knowledge, Excerpta Medica Database (EMBASE), SCOPUS, Latin American and Caribbean Health Sciences Literature (LILACS), Chinese National Knowledge Infrastructure (PsycINFO), Chinese National Knowledge Infrastructure (CNKI) and ScienceDirect. Preliminary search was carried out on 30 July 2020 and will be updated in March 2021. No restrictions on publication date, study location or languages will be considered in this review. The preliminary research strategies were carried out on 30 July 2020 and will be updated in February 2021. To measure the agreement between reviewers at each screening stage, Cohen’s Kappa will be calculated. Primary outcome will be factors related to suicidal behaviour in adults during COVID-19 pandemic. Grouped standardised mean differences and 95% CIs will be calculated. The risk of bias in observational studies will be assessed using the Methodological Index for Non-Randomised Studies (MINORS). Statistical heterogeneity will be assessed with the I2 statistic.Ethics and disclosureEthical approval is not required, as primary data will not be collected. The findings will be disseminated through peer-reviewed publications.PROSPERO registration numberCRD42020208816.